Matic, who arrived at Old Trafford from Chelsea at the start of the season, was substituted after 55 minutes of United's 4-2 win at Watford in mid-week with Mourinho saying the Serbia worldwide had a muscular problem.
"I play a game at a time", the United manager said at his pre-match press conference on Friday, when asked whether he was concerned about City's lead at the top. Mourinho's team failed to score in the past two visits to Emirates and won just once in the previous five travels to London, so I am sure the Portuguese tactician would be happy with a point from this clash. "Yesterday I was watching an interesting movie - Bjorn Borg v John McEnroe - and Bjorn's coach was telling him that all the time: one point at a time, think just about one point, and I tell my players [to] think just about the game".
"It doesn't matter what comes after, it doesn't matter what happened before".
"We don't think how many points we are in front of them, how many we are behind the leaders".
Paul Pogba insists he will be happy to let Ashley Young take Manchester United's free kicks against Arsenal, assuming he is feeling confident enough to try his luck again. Four points and two places separate the fierce rivals but, despite their lowlier league position, Arsenal are favourites given their home advantage and the fact they haven't lost to United during Mourinho's reign. "We don't think about that, just Arsenal".
"I can see Arsenal scoring goals against United and I find it harder to believe that United will score goals against them".
Pogba, 24, has played 90 minutes in United's last two Premier League clashes. Although they are not in the mix for the title at the moment, Wenger's team is looking to secure the Champions League football next season, and a win here would boost their morale and chances of doing so.
Either he starts Alexis Sanchez at the tip of the Arsenal attack like he did in a game against Manchester City or he plays the Chilean in his usual role on the flank with Giroud leading the line as a traditional striker.
Phil Jones, Eric Bailly and Michael Carrick could all remain sidelined for Saturday's tea-time trip to The Emirates Stadium.